Referring to FIGS. 8C and 8D, top and bottom views of a chip on lead package prior to encapsulation are shown. FIG. 8C shows the die 12 resting on the leads 88. Wire bonds 16 are used to electrically connect the bond pads (not shown) on the die to the leads 88. In FIG. 8D, the die 12 is again shown positioned on the leads 88. To increase the surface area upon which the die 12 is positioned, one or more of the leads 88a and 88b are extended as shown. For the sake of simplicity, the die attach film 54 is not shown in FIGS. 8C and 8D.
A leadless leadframe typically includes a plurality of die attach pads (PADs) arranged on the leadframe. A plurality of contacts are positioned around each PAD. The PADs and the contacts are held together by tie-bars. An adhesive tape is placed on the bottom of the leadframe, under the PADs and contacts. During the packaging process, a semiconductor chip is placed on each PAD using an adhesive or solder. Wire bonds are then formed between the chip and the contacts surrounding each chip. After wire bonding, the entire leadframe including the individual chips and wire bonds are encapsulated in a molding compound. The adhesive tape on the bottom of the leadframe is next removed, exposing the bottom surface of the PADs and the surrounding contacts. The leadframe is finally cut along the tie-bars, singulating the individual chip packages. The package is typically mounted by aligning the contacts of the package and soldering the bottom surface of the PAD to matching contacts on a printed circuit board. For more information on LLPs, see National Semiconductor's Application Note 1187 entitled “Leadless Leadframe Package (LLP)”, incorporated by reference herein for all purposes.
In spite of the fact that LLP packages do not have leads, the packages are still too large for many applications. As a consequence, packaging engineers are striving to make the packages thinner and to have a smaller footprint. One known approach to making the package smaller is to eliminate the PAD for each package. By doing so, the height of the package can be reduced. With this type of package, the chip is mounted onto the adhesive tape, wire bonded, and then encapsulated. The problem with this type of package is that the chip will often move relative to its surrounding contacts during encapsulation. This movement may cause the wire bonds to fail, resulting in low packaging yields. This type of package is therefore less than ideal.
An apparatus and method of making reliable miniature semiconductor packages having a reduced height and footprint is therefore needed.